Generally, in a wireless communications system, such as a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications system, there are physical data channels and physical control channels. The physical control channels may convey information to assist data communications, which occur over the physical data channels.
FIG. 1 illustrates a communications system 100. Communications system 100 may be a 3GPP LTE compliant communications system. Communications system 100 includes an enhanced NodeB (eNB) 105, which may also be commonly referred to as a base station, base transceiver station, controller, communications controller, and so forth. eNB 105 may control communications to and from a user equipment (UE) 110. UE 110 may also be referred to as a mobile station, terminal, user, subscriber, and so on. Communications from eNB 105 to UE 110 may occur over a downlink (DL) channel, while communications from UE 110 to eNB 105 may occur over an uplink (UL) channel.
A hybrid automatic repeat request (HARD) mechanism is a mechanism in a 3GPP LTE compliant communications system that allows a transmitter of a data packet (e.g., an eNB) to retransmit the data packet if a receiver of the data packet (e.g., a UE) fails to decode it. The eNB may add a cyclic redundancy code (CRC) to a transport block and transmit the data packet. Upon receipt, the UE may attempt to decode the data packet. If the data packet passes CRC check, then the UE may feed back an acknowledgement (represented as ACK or A) to the eNB. If the data packet fails CRC check, then the UE may feed back a negative acknowledgement (represented as NACK or N) to the eNB. If the eNB receives a NACK, the eNB may retransmit the data packet.
If the UE fails to locate a transmission intended for it, the UE may feed back a discontinuous transmission (represented as DTX) to the eNB. The DTX state may be fed back in a manner that the UE feeds back nothing (e.g., keep silent) to the eNB transmitter. If the eNB receives a DTX and if the eNB transmitted a data packet that corresponds to the DTX from the UE, the eNB may retransmit the data packet. However, if the eNB receives a DTX from the UE and it did not make a transmission to the UE, then the eNB may chose to not respond to the DTX.
FIG. 2 illustrates a prior art physical channel structure of a 3GPP LTE compliant communications system. As discussed previously, communications systems communicate over a DL channel (shown in FIG. 2 as channel 205) and an UL channel (shown in FIG. 2 as channel 210).
In a 3GPP LTE compliant communications system, multiple channels may be multiplexed over a single set of physical channel resource(s). Both control signaling and data may be carried over a single set of network resources. As shown in DL channel 205, control signaling may be carried in a first portion of network resources (shown as physical downlink control channel (PDCCH)) and data may be carried in a second portion of network resources (shown as physical downlink shared channel (PDSCH)). The PDCCH may include indications of network resources assigned to UEs. For example, indicator 215 may be an indication to network resources 216 assigned to a first UE, and indicator 218 may be an indication to network resources 219 assigned to a second UE, and so forth. In general, a UE detects its PDCCH and then determines a location of network resources allocated to it by the eNB and detects data transmitted to it at the location of the network resources. If the UE fails to detect its PDCCH, the UE cannot receive a transmission since it does not know where to locate the transmission. The UE may feed back a DTX to the eNB. If the eNB has not scheduled any transmissions to the UE, then there may not be a PDCCH intended for the UE.
UL channel 210 may be used to convey HARQ acknowledgements from the UEs in the 3GPP LTE compliant communications system, potentially with other information. As an example, network resources 225 may be used to convey HARQ acknowledgements from the first UE and network resources 226 may be used to convey HARQ acknowledgements from the second UE.